I just wanted to share what I did to prep my 2018 Suburban for towing my camper.
Under normal driving (no towing) my transmission temperature stays around 195F - 198F. When I first tried towing my 5000 lb camper, the temperature went up to 210F on a slight incline after a 2-hr drive. So I stopped towing with my 2018 Suburban and just used my 2001 Suburban with 285k miles that came with the heavy duty trailering package equipped with external cooler (KNP) and GT4 (3.73 gear). The 2001 did very well on a 5 hour trip to Pensacola, FL this past week.
After researching, I found out that the 2018 Suburban with the 6L80E has a transmission cooler thermal bypass valve from the factory. It does not allow fluid flow to the cooling lines to the transmission cooler located on top of the hvac condenser until the fluid temp reaches 190F. So basically, the fluid is recirculated back to the transmission without passing thru the cooler in the front. Good design to get the fluid up to operating temp fast. When the fluid temp reaches 190F, it opens up the line to the cooler and supposedly will drop the transmission temp down. But I think the bypass opening is proportional to the fluid temp. So who knows when it opens up fully. (maybe 230F ?)
I searched the internet for 6L90E transmission products to get around the thermal bypass. I found a few youtube videos.
1. One recommended to pull out the bypass valve (GM# 1351136) tap the hole and install a plug to the bypass hole.
This keeps the line to the cooler always open. The drawback is it will take a while to get the fluid to operating temp.
2. Mishimoto low temp thermal bypass valve. Included with the cooler kit. Very expensive at $400.
3. I found a product STL010 Sure Cool transmission system upgrade that is meant to replace the thermostat inside the bypass valve. Reasonable at $43.
I went with Option# 3.
So far so good after the test drive.
Normal driving, my transmission temperature stayed at 158F - 160F. (see attached pic)
Towing transmission temps still remains to be seen later.
Under normal driving (no towing) my transmission temperature stays around 195F - 198F. When I first tried towing my 5000 lb camper, the temperature went up to 210F on a slight incline after a 2-hr drive. So I stopped towing with my 2018 Suburban and just used my 2001 Suburban with 285k miles that came with the heavy duty trailering package equipped with external cooler (KNP) and GT4 (3.73 gear). The 2001 did very well on a 5 hour trip to Pensacola, FL this past week.
After researching, I found out that the 2018 Suburban with the 6L80E has a transmission cooler thermal bypass valve from the factory. It does not allow fluid flow to the cooling lines to the transmission cooler located on top of the hvac condenser until the fluid temp reaches 190F. So basically, the fluid is recirculated back to the transmission without passing thru the cooler in the front. Good design to get the fluid up to operating temp fast. When the fluid temp reaches 190F, it opens up the line to the cooler and supposedly will drop the transmission temp down. But I think the bypass opening is proportional to the fluid temp. So who knows when it opens up fully. (maybe 230F ?)
I searched the internet for 6L90E transmission products to get around the thermal bypass. I found a few youtube videos.
1. One recommended to pull out the bypass valve (GM# 1351136) tap the hole and install a plug to the bypass hole.
This keeps the line to the cooler always open. The drawback is it will take a while to get the fluid to operating temp.
2. Mishimoto low temp thermal bypass valve. Included with the cooler kit. Very expensive at $400.
3. I found a product STL010 Sure Cool transmission system upgrade that is meant to replace the thermostat inside the bypass valve. Reasonable at $43.
I went with Option# 3.
So far so good after the test drive.
Normal driving, my transmission temperature stayed at 158F - 160F. (see attached pic)
Towing transmission temps still remains to be seen later.
